Hi @ramin sa ,
what do you mean with trusted forest? Kerberos authentication working?
If so, then you to manually install the agent and point it to the management server properly.
Please read this carefully:
Install Windows Agent Manually Using MOMAgent.msi
https://learn.microsoft.com/en-us/system-center/scom/manage-deploy-windows-agent-manually?view=sc-om-2019&WT.mc_id=EM-MVP-5002219
If you are doing the so called "Pushh Install" then you need to ensure that the account you are using has admin permissions on the targeted systems and also that RPC ports are opened towrads the targed systems:
Install Agent on Windows Using the Discovery Wizard
https://learn.microsoft.com/en-us/system-center/scom/manage-deploy-windows-agent-manually?view=sc-om-2019&WT.mc_id=EM-MVP-5002219
Please read both articles, they will give you all the details yoiu need in order to install SCOM agents one way or the other.
----------
(If the reply was helpful please don't forget to upvote and/or accept as answer, thank you)
Regards
Stoyan Chalakov