Strfry has no support to set an icon, afaik. At least last I checked...
Discussion
I've read somewhere (can't find it again) that you could direct that specific traffic through reverse proxy to fix it.
And if you check relays running strfry some do have custom icons.
To issue for me right now is that I'm running it through cloudron tunnel and no reverse proxy like nginx / Caddy or similar.
Here it was!
But can't figure out how to implement this with cloudflare tunnel.
If you have a github account, you could request this to be added to the "Relay Document" as served by strfry and reference this: https://github.com/nostr-protocol/nips/blob/23d605140bdbe6ccc43c6ebbcd2412a05ff262fa/11.md?plain=1#L259-L268
Hope it helps. :)
Thanks. I thought about it and also asked in the telegram group! We'll see if I get some response there first.