Take each thing seperately, in other words connect them directly to your computer first. Normally only 1 thing on a network should be a DHCP Server. But often a router will have a WAN port and and another router will be plugged into that. In that case the "another router" can run DHCP and will assign that to 1st router. 1st router now knows how to get to "another router" (2nd router). Which should allow you to get to it from 2nd router.
You can't talk to another /24 network if your computer is not on that /24 (aka Class C - 255.255.255.0). The 1st three octets have to match. Unless ... there is a router inbetween your computer and "another /24 network" - that is on both /24 networks. In that latter case that router inbetween has the route to the "another /24 network" and can get you there.
To configure router gear where DHCP isn't working plug directly into it on ethernet switch or LAN port. Knowing it's IP Address you have to manually configure your computer (take it off of Automatically) to match the 1st three Octets (1st three of the dotted decimal numbers) and with a 4th octet in the range 1-254, because .255 is the broadcast address. Make sure you pick a 4th octet that is not in use to your best knowledge. Not the ip of the router, or anything else that you are aware of on the network range. I usually pick .10 because normally nothing is on the lower end of a dhcp range.
Anyway hooked up directly and manually IP address set, you should be able to go about changing IP Address of a router or access point. Keep in mind if you change it outside of the /24 subnet you and it WERE IN that you will lose access to it again. And will have to change your manually configured IP Address again. Or go back to automatic - if you have now also enable DHCP on that router device.
Note that for an access point (range extender?) it doesn't usually matter that it is on a seperate /24 network ... as it doesn't operate at Layer 3 (Network, IP Addresses and such) anyway. It just switches Ethernet / Wireless Ethernet frames anyway - all of the IP stuff just transparently passes through it. You probably get DHCP from your 1.1 router ... and talk the local network and Internet just fine. You could use the above MANUAL IP method whenever you want to look in the wireless access point. But unless it's broken / not working, you shouldn't have to. Access Points normally don't do any routing at the IP level and don't run DHCP - so all of that simply doesn't matter. Of course you might like it on the same network range (/24) as your other router for ease of maintenance. Just don't plug into a WAN port, plug into a Switch/LAN port on your main router.