How to get value of 1 segment value into another value set of a segment ?

Hi,

we are creating a process to streamline the payment of our Gym reimbursement. Currently it is paper based and having many issues where payments to users cannot be tracked. This process is being catered in HCM using Special information types.

This SIT contains 3 segments, where the user entered amount 1 and amount 2 in segment 1 & 2.

The values in the segment 1 and 2 are then required in 3rd segment as a SUM of segment 1 & 2.

we have searched in knowledge base but no such solution has been found.

Kindly guide on the subject query.