It’s in the “Advanced” section, “Configure how Tor Browser connects to the internet”.
I believe this should work.
I am not sure about the specifics of how dumbproxy works, but if it really is just an HTTP proxy, then this setup should work.
Otherwise you can consider GitHub - serjs/socks5-server .
If you don’t care about privacy that Tor Browser provides and only want to circumvent the blockings, you can set up any other browser to use a proxy.
If you’re feeling adventurous / generous, you could set up a Tor bridge instead for others to use as well. Since you have a domain, a WebTunnel bridge would perhaps be nicer.