Hi flower!!
What is the vendor of your repeater? But, though, i’ve never seen a repeater which can support only one channel… Even the cheapest allgons have two-channels… But answer to your question: you can’t do it by tuning your cell (in common)
I think you should try to solve this problem from the other side:
1\ try to reconfigure your repeater or
2\ find another cell to link repeater (with one tre) – but i wouldn’t advise to do it…
good luck!!