The numbers are out of range for a passcode, let’s start by using Atbash on the whole string

3n7auarsade9s5g6

Make a 4×4 grid

Read up from the lower left S

sau35danger769sa

Invalid. Remember that we used atbash so we need to find the opposite of danger which is safety

sau35safety769sa

Make a 3×6 grid

Doesn’t look like a passcode but if you try to find the 8 letter keyword you can spot conspire. We need to rearrange the rows in the right way.

Shift row 1 left by 1, 2 right by 1, 3 right by 1, 4 left by 1, 5 left by 1 and 6 right by 1

Read down from the upper left G

ghg49conspire425qu

There are a few pointers in there, twice eve is repeated which could be seven. Let’s split things up

up eve hgievidlo eve ruojrp

See how following eve you have ghi and ruo. Reversed eight and four maybe.

Let’s reverse the string and spot the numbers

prj our eve old ive igh eve pu

Clever, they used three letter numbers and skipped the first letter

prj four seve old five eigh seve pu

prj47old587pu