https://help.gosimpletax.com/hc/en-gb/articles/115000027404-Where-can-I-enter-Adjustments-to-Partnership-Profits-to-reduce-the-Class-4-National-Insurance-I-need-to-pay-
Some adjustments can reduce the amount of Class 4 National Insurance contributions you have to pay.
These include:
• adjustments for changes in accounting practice
• certain losses from earlier years
• employment earnings included in your profits
Click on the Partnership Page
Click on EDIT
Click on NATIONAL INSURANCE
Enter the ADJUSTMENT VALUE
Click SAVE