update mainform from subform

Is it a problem that this donorid_tx isn't in another subform with the table it belongs to as a recordsource?

No. The problem is that you appear to be duplicating data.  That is why you are getting the advice you are getting. The only main form (parent table) field you need in the child table bound to the subform is the foreign key which points the child table to the parent table.

If when you open the child table in DS view and sort on donorid_tx, you see "duplicate" instances of donorid_tx and donorid_tx is NOT the foreign key, then it doesn't belong in the child table.

Can you load up a sample db so we can get a better understand of what it is you are trying to accomplish???

ET

Thank you all for the super helpful responses.
I figured it out though I'm not sure how. <so many tries>Code posted below.

Curious as to why the record source for the main form continuously updates/changes as a query the more things I add. What does this mean for the database? Is that something back-end I should never mess with? I know it's a rookie question but a rookie I be.

The donorid_tx is a foreign key and so duplicates are allowed.

The first subform (query based) looks-up previous donors associated and then I wanted to select from this list and transfer data to 2nd subform in order to assign that donor to an instance (in a table). I cannot post, it holds health-sensitive information. However I will post the code below for my onlick event in the first form which correctly transferred the value and verified the transfer.

Again thank you all so much.

Private Sub Command39_Click()
Forms![mainform]![subform1]![subform1fieldtobetransferred].Value = Forms![mainform]![subform2]![subform2fieldtobegained].Value
'Provide the user with the option to save/undo
'changes made to the record in the form

    If MsgBox("Selected donor for this record" _
        & vbCrLf & vbCrLf & "Do you want to save these changes?" _
        , vbYesNo, "Changes Made...") = vbYes Then
            DoCmd.Save
        Else
Exit_cmdCancel_Click:
Exit Sub
    End If
End Sub

If you don't have a lot of data in the database, it would be good to post the whole thing.  Since the data is sensitive, you can obfuscate it.  I generally replace all last name fields with just the first letter, and same for all addr1 fields.  SSN's I generally change to all zeros.  There may be other identifying fields you need to hide but otherwise leave the base data alone since it gives us perspective.  Sometimes if there is too much data, I might strip out most of it.  That is harder though since RI always gets in the way.

You said that DONORID is the PK.  Sounds like donorID_tx is not the FK.  Usually the PK and FK names are identical although some people add suffixes suck as donorid_fk.