Auto fill one multiselect question from two or more previous questions

How can we auto fill multiselect question based on responses from previous multiple questions? I understand that one can use if (${Q1=‘1’, ‘1’, ${Q1) to auto fill Q1 in Q2 for instance.

However, if we want to auto fill answers at both Q1 and Q2 in Q3, how do we go about this? What does (${Q1=‘1’, ‘1’, ${Q1) becomes in this case?

Welcome to the community, @aij_erc! Could you also list a dummy question for Q1, Q2, and Q3 along with its dummy choices so that the community can also understand what the choices look like? This should help the community to understand your query pictorially and hence should be able to help you out accordingly.

Assuming I have:
Q1 Which brands are you aware of?
Brand 1
Brand 2
Brand 3
Brand 4
Brand 5
If answer to Q1 is Brand 1 and Brand 2, I want to prompt for Brands 3 to 5 at Q2
Q2 Are you aware of the following brands?
Brand 3
Brand 4
Brand 5

Assuming Brand 3 and Brand 4 are selected at Q2, I want Q3 to auto fill selected answers in Q1 and Q2.

Q3. Autofill total brand awareness
Brand 1
Brand 2
Brand 3
Brand 4

I am assuming, you already know how to filter out brands selected in Q1 not to appear in Q2 (basically using choice_filter). Now that this has been achieved, Add this expression concat(${Q1}," “, ${Q2}) in calculation column of Q3. Optionally make Q3 read_only column of the xlsform to " yes” to disable the question from accidental change by the user. Let me know if this solves your issue.

Thank you so much. It really worked.