We will use two Excel tables for example: "Courses" and "Students".

Create a new project using the "Import data" option.

Tables imported successfully.

Please note that the values in the “Course” and “Subject” columns are the same in both tables.

Go to the "Students" Form Builder and add a new field to the form.

We need to create the Relationship field. We select the "Courses" table, the "Course" column , relationship type is many-to-one / drop-down list.

Next you need to open the field editing page. To do this, use the context menu and select the "Edit" item.

On the field editing page select the "Relationship settings" tab.

Here you need to select the Link column in the current form ("Students"), which values coincide with the column in the "Courses" table.

Click the Update button. The records will be linked automatically.

Now you can delete the "Subject" column if you need.