Forms have several trigger options. You can find them all in Forms > Widget > Behavior.
You can trigger a form to appear at certain points on your page (50%, 70%, etc), or you can set your own trigger point with an anchor tag.
To do this, first create an anchor tag at the point you choose on your page.
Then, copy the tag you’ve created. In your widget’s Behavior settings, check the Show when user scrolls to… box. Then select the drop down and choose an anchor.
Paste your anchor tag in the widget’s anchor field, and save your settings.
You’ll now see your widget appear when you scroll to the anchor tag you’ve set on your page.