Start the tape and patch a -5 to +5v static source to that. Flick down on the toggle to set first cue, up on the toggle to set second cue. Looping will start automatically. Press record. The time between your down up is delay time. At 0v the delay will accumulate infinitely and clip the output eventually. Positive volts results in destructive looping, negative volts is slightly different, but sounds similar.
I’m not at my rack, but I think that’s it.