Adding a file to an exisiting repository from command line

Hi… sorry I am very new to GitLab and I can’t seem to add a file to an existing repo…

there is a repo

git@mycompany.com:ECSE/AWS/masterpayer-assumerolefunctions.git

I appear to be owner… but I did not create it… there is a folder under this called /lambda-functions

I created a new lambda function that I want to add to this folder…
git remote -v
origin git@gitlab.mycompany.com:ECSE/AWS/masterpayer-assumerolefunctions.git (fetch)
origin git@giblab.mycompany.com:ECSE/AWS/masterpayer-assumerolefunctions.git (push)

but
git push origin master
git@gitlab.mycompany.com: Permission denied (publickey,gssapi-keyex,gssapi-with-mic).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

I copied the line from the web site… but I am also not sure how to put it in the folder /lambda-funcions
I have made my own projects and added to them, but this is a project someone else started and I just want to add one file to it. Probably going about it all wrong as I am a newb… anyone that would take pity and tell me what I am doing wrong I would appreciate it. As I said, I appear to be the owner and we are a small team and are all owners as far as I know so I don’t think its permissions - but is the syntax I am using to get to that folder incorrect.

Thanks
Bill