This is one of the limitations of a service file, which you may or may not have seen. If a soldier was present on roll when a regiment participated in a military action, it's reasonable to assume that he was involved. If he was absent, the opposite is true, but these are assumptions. Unless the soldier is reported as killed, wounded or captured in a military action, it's an assumption, and probably the only one you can fairly make.

If rolls for the period in question have been lost or destroyed, you can't really guess about this. Unless, of course, your ancestor was discharged, died or was taken off roll earlier.

In any case, you'll need to start with the soldier's service file and match it to the regimental history.