Hi @MuzaffarMahmood ,
Could you tell me the field's data type that you want to use this combo box to update?
If it is a choice column, please clarify whether it is multiple choice.
1)If it is a text type, please set the field data card's Update:
Concat(combo box name.SelectedItems,Result&",")
2)If it is a single choice, pleae set the field data card's Update:
{Value:combo box name.SelectedItems.Result}
3)If it is a multiple choice, pleae set the field data card's Update:
RenameColumns(combo box name.SelectedItems,"Result","Value")
Please replace combo box name with the name that you use.
To sum up, different data type need different formulas to update.
Here's a doc about how to update complex data type of sharepoint list in powerapps for your reference:
https://powerapps.microsoft.com/en-us/blog/default-values-for-complex-sharepoint-types/
Best regards,