Place the appropriate-sized tape reel on your tape machine and put the machine in playback mode. Listen to your recording and identify what adjustments you want to make the recording. If you are adjusting the tape speed to fix the pitch of a recording, increase the speed to pitch up and decrease to pitch down.
Locate the pitch control function on your tape machine. This is usually a large knob with "+" and "-" symbols to show you which direction speeds up and slows down the tape. If you do not have pitch control on your tape machine, you won't be able to adjust the pitch.
Play back the recording and adjust the pitch with the pitch control on the machine. If you are adjusting the pitch to be in tune with a live player have them run through it a couple times to make sure you have adjusted it correctly.
Record the effect with another device--you can run the tape deck into your computer, for example, and record it with recording software.