Yes there is.
Connect the tape deck input to the amps tape 2 record output.
That will send a fixed level output of whatever you are playing into the tape deck.
If the tape deck has a source tape selector then setting it to source should get the meters working.
If it doesn't you may have to get the deck into record mode to see the input on the meters. You may need to put a cassette into the deck to get it to do that and it isn't a great idea to leave it in record/pause for continuous use of the meters.
You should be able to find the manuals for the amp and tape deck online.