The routers must be able to route the client requests from the network of the client to the network of the DHCP server. One such simple router rule is the IP helper. The helper just tells the router to forward the DHCP requests to the known IP address of the DHP server.
For PXE requests, you just need to configure the routers to forward the client request to the PXE server, just like you do with the DHCP server. Locate your router, find the DHCP IP helper entry, and add another entry that looks exactly like the first one but uses the IP address of the PXE server. For more information, see the blog post You want to PXE Boot? Don't use DHCP options.
Besides, you can add an IP helper entry for each PXE server. In a load-balancing scenario (multiple PXE servers), PXE servers can be up or down in a group, and you don't have to do any extra configuration. In diverse environments (Windows, Linux, and Router PXE servers all coexisting), the different PXE servers can selectively respond to the clients that they recognize.
--If the reply is helpful, please Upvote and Accept as answer--