Out of the box, when you create a custom table it will create 4 fields for when the record was created and who created it, as well as when the record was updated and who updated it.
You can perform a check on any of those fields if you want. The simple solution would be to place a macro in the enabled property of the fields. You can find the enabled condition in the Field advanced settings when you select a field in your custom table.
So say you have a field called Name. In the Enabled condition you enter
ItemCreatedBy.Value == CurrentUser.UserID || ItemCreatedBy.Value <= 0 So now when the form loads if the user who created it is the one editing it, it will allow them to edit it. The
<= 0 comparison is for inserts so the field is enabled.