When using large delta mass lists (such as during charge variant analysis) or large mass error tolerances the intact mass software will label the closest mass to the theoretical value. With supplemental sample knowledge, you can manually reassign the mass label to other delta masses within the delta mass list.
To do so *right click* the mass in question with the mass table and select 'Choose match within details'.
A new pop-up will appear displaying all the delta mass assignments that meet your matching criterial and you can select an alternate assignment to replace the current one:
The Dalton error between the mass and calculated value will also be displayed, along with a label for the original assignment it was matched to.