you can’t ! I should have clarify this point, you are right : you must stop the BBH and use No-Hopping.
However I must admit that pushing more traffic to TRX1 does not serve much purpose apart from checking that this is not a HW failure on TRX 3 and TRX 4 (as those are the ones on which there was enough traffic to be able to analysie RMS reports)
There is no real point in finding which one of the 4 frequencies is interfered : they are probably all equally interfered, assuming you are using the same BBH MA-list in the neighbours too.
If your BCCH planning is different than your TCH planning, then you might see a little difference by going from BBH to NH and pushing traffic to BCCH.
Notice that I proposed other things you could try in interferer and interfered cells.
In the RMS C/I report, you may find which cell is interfering.