Server connection error when reinstalling High Sierra on my iMac

How do i fix the problem on my 2011 imac where when i try to reninstal high serria from internet recover it says server cannot be connected. I did basic trouble shooting with associate but to no avail. This started when I fully cleared the disc drive cause I bought it off somebody and now the only way I can boot it up is through the recovery system. I tried everything I’ve tried resetting the NVram. I tried doing a few things in command prompt just. I’ve been at this issue for years So please help New Serra community