Hi @Anonymous ,
If you're using a SharePoint Online list as your data source, (and possibly CDS as well, I think), they already record this information for you in the 'Modified By' and 'Modified' columns. All you have to do is display them on your form.
If you're using something else that doesn't already do this, then you may have to create those columns yourself and populate them with the data you want when the user submits the form.
With the columns created you can add the data cards to the form, pre-populate them with data and then hide them.
For the Modified By data you can create a simple plain text column in your source (let's call it ModifiedUser). In the form, once you've refreshed the data source and added the ModifiedUser column as a datacard, the datacard Default: property should be ThisItem.ModifiedUser. You can override this by unlocking the data card and changing it to User().Email
For the Modified column create a date column in your source - if you can, otherwise plain text will also work, you'll just have to convert from text to date when you want to perform date functions. Let's assume this column is called ModifiedDate.
As before, refresh the source, add the column to the form, but this time change the Update: property to Now()
The only reason I use the Update property on the date is that if this is time sensitive and the person takes two hours to edit the form, Now() on default will record the time from when the form was initially rendered.
Update should only apply it as the form is submitted.
Hope this helps
RT