problems using a lookup in a stateless form

problems using a lookup in a stateless form

I have a table <MyTable> which has a lookup to another table <Data Table>- so far so good.

I have a stateless form which receives the ID of the row in <MyTable> via a function.

I can then pull the row in <MyTable> and populate the stateless form. I need to be able to populate the Lookup with an existing value from <MyTable> and allow the user to change the lookup value in the stateless form - eventually to save back to <MyTable>.

Currently the stateless form has a lookup defined in a similar way to <MyTable> --> <Data Table>

The trouble I have is:
1. Simply pulling the existing lookup value from MyTable gives me a string which is the current value of the Lookup.
2. I can find the ID of the Row in <Data Table> for the current value but cannot find how to set it in the stateless form Lookup as set, while leaving the functionality of the lookup.

Can anyone help here?