Intro and emissions help

[Mdkrp1]

Hi All-
I just jumped into the classic 911 madness and loving it so far. I have learned much from Pelican and another site to date.
I recently purchased a Black/Tan 1987 911 3.2 coupe with 117k miles and had a top end repair several years ago which is mostly stock with a few tasteful mods the prior owner did-
M&K pre-muffler and sport muffler with a SW chip running 93 octane. The prior owner does not believe the pre-muffler had a cat converter in place but we really dont know.

The car was in TX at sea level and now its in AZ at approx 2300 ft elevation. Unfortunately, we don't have 93 octane avail - only 91. I took it for emissions and it failed twice (once without any adjusting and 2nd after my local P car mech did some adjusting). He felt the mixture was too rich but could not do much else at the time.
Both times, the car was warmed up properly.

IT did pass the hydrocarbons emissions but failed both times the carbon monoxide; not by much but still by enough to fail.

I am now looking to replace the 93 chip to one that is stock but also in need of other ideas/suggestions so I can get the car to pass and get registered.
Any help is appreciated!
many thanks