two hAP into one wifi

Dear,
I would like to ask you for little help with my problem.
In house I have one RB- 3011 which is main router (DHCP, firewall, etc.) for the house, hAP device which is in AP mode and it does IoT wifi for end devices. Outside of the house is shed where I have some IoT devices which need wifi but there is really bad signal (about 20%, it’s about 15-20m from hAP). There I want to add next hAP but I don’t know how it configure. I want to only one wifi networks.
I tried repeater but the devices in the shed connected to main hAP not to the second in the shed.
Could anybody help me with the problem, please?

thank you and have a nice day.