natting an outside local subnet

Hello redditors!

I have little experience doing NAT on an CISCO asa 5510 (yes it's old). I have been able to NAT inside local but on this particular situation I have not been successful, and so I have turned to you for help.

Scenario:
We have a VPN tunnel setup for a third party with a destination range 192.168.100.0/24 . We are starting a new service with another party that has the exact same destination subnet, I have been asked by the 3^rd party to NAT their subnet. Can this be accomplished on my end or do I need to have the 3^rd party NAT their subnet? This is what I have tried:

access-list policy-nat-test extended permit ip 192.168.100.0 255.255.255.0 10.2.1.0 255.255.255.0 access-list policy-nat-test extended permit ip 192.168.100.0 255.255.255.0 10.2.1.0 255.255.255.0 access-list policy-nat-test extended permit ip 192.168.100.0 255.255.255.0 10.2.1.0 255.255.255.0 static (OUTSIDE,INSIDE) 10.2.1.0 192.168.100.0 netmask 255.255.255.0 

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