With the Cyclus Tools tap Professional for BSA thread (1.370" x 24 tpi) you create an optimal coaxiality of the thread in the bottom bracket shell.
Screw in both sides of the tap at the same time to prevent canting and thus damage to the existing thread.
Use a cutting oil suitable for the material to be machined.
Please note: Letters or marks on the tool always refer to the tool itself. I.e. if an "R" is applied to one side, this is a classic thread with the direction of rotation to the right - clockwise. Similarly, if an "L" is applied, the direction of rotation is to the left - counterclockwise.
The application side of the bicycle can never be meant. Since there is no fixed reference system here!