Extract from Dx7 manual:

In the Slave mode, the DX7 is used as a slave radio in conjunction with a Spektrum® radio that is used as the
master that is in P-LINK mode; there is no need to match the slave’s programming to the master transmitter’s
programming in this mode.

If you use a Spectrum (or a JR with P-Link like the 2610) there is no need to touch the trims on the slave.

Terry