Creating a Single WiFi Network with LTE Huawei CPE B593 and Asus RT AC51U Routers

Hello.
I have a lte huawei CPE B593 router located on the floor which means that I have poor coverage on the ground floor. I connected a second asus rt ac51u router with the cable at the bottom but now I have two wifi networks. and here is the question, can there be only one network? if so, please give me a very "pathological" step-by-step explanation of what to do. best regards.

It can't be done like that, you can give them the same name and password, windows will choose the one with the stronger signal, but to say the least it works. (although it depends how it goes)
With this equipment you only have one option - two WiFi networks.
Not a book option, lightly hide this router at the top so as to weaken its signal at the bottom (because there is probably no WiFi power change option), windows should switch to the lower network faster.

Exactly.
And as I wrote above, you can help windows to "choose" the network, weakening the one on the floor, put the router in the corner wall / wall or lightly hide it behind the cans after the hop drink / aluminum foil / ESD foil, should effectively suppress the signal so that windows on the ground floor did not have a "dilemma" with which network to connect - because it will be the most annoying at such distances, the signals may overlap 50/50 and it will wander from network to network every now and then losing connection.
The lower router should be placed as centrally as possible so that the signal does not change too much when moving the computer on the ground floor.

there is a problem because ip camera is connected and it works over that wifi network. the computer in which I would like to amplify the signal is downstairs and it is recording but the internet is slow so I have to have the same network. I have 30mb internet connection and the bottom speed is 1mb max.

Routers are connected by a cable, so I don't understand why speed degradation?
In that case it would be better to give 2 network names and use the lower one and the upper one at all to throw them out of the default ones in Windows.
Upper AP for camera - 1 name
Lower AP for computer - 2 name
In windows, remove the upper one from remembered networks.

The network will still be the same, provided that the routers are connected via LAN ports, you may have trouble getting into the camera via WAN.

yes, only if I have a second network, I don't have a camera image on my computer because it uses wifi on top. unless you can work around it somehow

Added after 3 [minutes]:

and I can't switch cameras because again it doesn't catch the router's range below and the camera is on the second building on the roof.

Connect the bottom router with a LAN instead of WAN port and disable DHCP on the bottom one (first).
You will have a picture.

Your problem is that you have an Asus connected to the WAN and acting as a router. Connect to LAN, give it LAN address 192.168.1.2 (if B593 has 192.168.1.1). Disable on Asus DHCP. The network name on Asus can be the same or different, the password and encryption the same. WiFi channel different. You will have one network in your home created by B593, all devices in it will see each other, addresses will be allocated by B593.

I just did everything as you wrote and I will tell you that it works thank you very much!!