Go to the Equity Plans > Pools & Plans page, find the pool you would like to increase, click the three dots on the right-hand side, and select Increase Pool.

Alternatively, you can click on the button + New Transaction > Pool Increase:

You can then add the date, amount, and other relevant information to the increase. Same as when creating a pool, you can also choose if the shares should come from authorized capital or reserved shares from a stakeholder.