this is a secret server mod it is only for the server folder!
since you do not have the -servermod command, we will use the old method, hide the secret file in the "Addons" folder in the server folder next to other pbo, since the secret file has no signature, it will not prevent players from entering the server, but it will work!

go to your server folder
find the "Addons" folder there
via FTP (file zilla)
server01 / Addons / HelicopterMod_SERVER.pbo
do not upload the file to the server through the file uploader in the file manager - in 90% of cases it will damage the file use ftp
after each update of the game version, for example, before dayz, the file will be deleted and it will need to be added there again

I remind you that this is a secret mod server, it cannot be upload to the workshop or transferred to someone else, otherwise the mod will be deleted