Help setting up home network - if feasible.

[Too Tall]

We have no fibre in my area as yet, so we're limited to ADSL at around 5mb.

I have however managed to connect with a 4g router giving me speeds of around 100MB which is sufficient.

The 4g router (Huawei B525) is in the loft (Wifi A).

Wifi A is hidden and is only used to manage the 4g router.

Downstairs I have an Asus RT-AC86U which is the main hub for the house - Wifi (B).

I have the 4g router connected to a GS105E switch in the study via ethernet cable ran in the walls.

My desktop connects via Ethernet to the same GS105E as does the RT-AC86U in the living room.

Herein lies the problem, the traffic from my pc goes via the switch to the 4g router, whereas i would like it to go via the RT-AC86U as the network storage is there.

Is there a way I can configure the GS105E to route my pc's traffic via the AC86U with my current configuration?

I could run another cable as oer the second image, but there is no more room in the conduit from the loft to the living room so it would a PITA.

 

[Too Tall]

All my traffic from my desktop goes directly through the 4g router, I am currently unable to access the RT-86U and the network storage which is connected via it.