How to fix broken lookup on the site

If your SharePoint list has a lookup column that was connected to a list which has been deleted, the field configuration will show an empty 'Get information from:' value. SharePoint does not allow you to select a new source list through the UI in this case.

This guide shows how to fix a broken lookup by running a script in the browser's Developer Tools.

To do this, follow these steps:
1. To ensure the script runs properly, the SP.ClientContext must be available. You can do this by using one of the following options:

• Open any customized form (New, Edit or Display) on the site.
• Go to Site contents and switch to the Classis experience
• Navigate to: <web-url>/_layouts/15/user.aspx.

2. Open Developer Tools (F12) and switch to the Console tab
3. Insert the following script into the Console tab. Before running it, replace the following variables in the script and click Enter:

• listWithLookupUrl - URL of the list with lookup
• lookupFieldName - Lookup name of the column
• lookupSourceListUrl - URL of the new source list you want to connect

(function updateLookupFieldSchema() {
    const listWithLookupUrl = 'https://m365x46891638.sharepoint.com/sites/ContractManagement/Lists/Contracts';
    const lookupFieldName = 'LookupToAccounts';
    const lookupSourceListUrl = 'https://m365x46891638.sharepoint.com/sites/ContractManagement/Lists/Accounts';

    const targetUrlObj = new URL(listWithLookupUrl);
    const sourceUrlObj = new URL(lookupSourceListUrl);
    const targetListSR = targetUrlObj.pathname;
    const sourceListSR = sourceUrlObj.pathname;

    const targetWebUrl = extractSiteUrl(listWithLookupUrl);
    const sourceWebUrl = extractSiteUrl(lookupSourceListUrl);

    const ctxTarget = new SP.ClientContext(targetWebUrl);
    const webTarget = ctxTarget.get_web();
    const listTarget = webTarget.getList(targetListSR);
    const field = listTarget.get_fields().getByInternalNameOrTitle(lookupFieldName);

    ctxTarget.load(field, 'SchemaXml', 'Id');
    ctxTarget.executeQueryAsync(onFieldLoaded, onError.bind(null, 'Load field'));

    function onFieldLoaded() {
        const xmlDoc = new DOMParser().parseFromString(field.get_schemaXml(), 'application/xml');
        const fieldNode = xmlDoc.getElementsByTagName('Field')[0];

        const ctxSrc = (sourceWebUrl === targetWebUrl)
            ? ctxTarget
            : new SP.ClientContext(sourceWebUrl);
        const webSource = ctxSrc.get_web();
        const listSource = webSource.getList(sourceListSR);

        ctxSrc.load(listSource, 'Id');
        if (sourceWebUrl !== targetWebUrl) {
            ctxSrc.load(webSource, 'Id');
        }

        ctxSrc.executeQueryAsync(function () {
            const listIdBraced = '{' + listSource.get_id().toString().toUpperCase() + '}';
            fieldNode.setAttribute('List', listIdBraced);

            if (sourceWebUrl !== targetWebUrl) {
                fieldNode.setAttribute('WebId', webSource.get_id().toString().toUpperCase());
            } else {
                if (fieldNode.hasAttribute('WebId')) {
                    fieldNode.removeAttribute('WebId');
                }
            }

            // fieldNode.setAttribute('ShowField', 'InternalNameOfYourColumn');

            const newSchema = new XMLSerializer().serializeToString(xmlDoc);
            field.set_schemaXml(newSchema);
            field.update();

            ctxTarget.executeQueryAsync(
                () => console.log('✅ Lookup field schema updated.'),
                onError.bind(null, 'Update field')
            );
        }, onError.bind(null, 'Load source list'));
    }

    function extractSiteUrl(listUrl) {
        const urlParts = listUrl.split("/");
        if (urlParts.length > 1 && urlParts[urlParts.length - 2].toLowerCase() === "lists") {
            return urlParts.slice(0, urlParts.length - 2).join("/");
        }
        return urlParts.slice(0, urlParts.length - 1).join("/");
    }

    function onError(stage, sender, args) {
        console.error(stage + ' error: ' + args.get_message());
    }
})();

Once the script runs successfully, your lookup column will be connected to the new list, and you’ll see the correct source in the column settings