This article shows how to amend the open float of a cash drawer/till for a specific day.
Go to Manager > Sales > Till Floats.
Find the date you wish to edit the float for, then select the 3 dots > Edit Open Float.
Enter the new float amount in the Edit Open Float calculator and click Ok to finish.
This will update the Open Float for the day you are editing and subsequently the Closing Float for the previous day.