Mscn -- "Hey guys, so I’m the most senior RCA in my office with about 4 others, one being a PTF. Two of my assigned routes on the matrix have the same relief day

Is there anything I can do to fix this?"
-- Your OP is a bit confusing, at least to me.
-- It will be on manglement to find a relief carrier should one of your routes need to be covered while you are covering the other.
-- What are your assignments on the Matrix? Primary, secondary, or tertiary?
-- Are any of the other RCAs on the Matrix in secondary or tertiary positions for your routes?
-- Moving on...
-- There are "about" 5 RCAs in the office and one - not you - is a PTF.
-- You might be senior time-wise in the office and career-wise with the other other RCAs, including the PTF, but when a regular route opens up, the PTF will get it or which ever route is left over after the bidding dust settles. Article 30.2.A.3. In part: a part-time flexible rural carrier cannot decline conversion to regular status.
-- Per the Matrix Quick Reference Checklist: A relief carrier can only hold one primary position. Can only be in three positions on the matrix. Can be in 2 secondary positions.
-- Inform manglement of the "conflict" as well as your office steward, and if none, your Assistant District Representative who may be able to help manglement straighten out the office Matrix.