If the only effect is sniffle/sneezes then I train, owt more than that (e.g gunky coughs, aches etc) then it's not worth making it worse.
Broadly speaking this is my approach too, although if I feel badly bunged up then I might wrap up warm and do something very gentle to unblock the pipes a bit.
Rest.
If the only effect is sniffle/sneezes then I train, owt more than that (e.g gunky coughs, aches etc) then it's not worth making it worse.