Grafana behind F5 - origin not allowed

We have 2 instances of Grafana
they are behind and F5 LB
Today we upgraded from 9.3.6 to 10.3.1 and ever since when accessing Grafana from the LB we get “403 origin not allowed” (accessing directly to the servers in port 3000 works fine)

I know there is a breaking change where you need to add http_host header but we are not sure where to add it in F5

would appreciate any help - Thanks

server config (grafana.ini)
;protocol = http
;http_addr =
;http_port = 3000
domain =
;enforce_domain = false
;root_url = %(protocol)s://%(domain)s:%(http_port)s/
;serve_from_sub_path = false
;router_logging = false
;static_root_path = public
;enable_gzip = false
;cert_file =
;cert_key =
;socket =

Have you got the solution for this ?