[ASK] How to do FTP Tunneling through other server

Hi Guys

I'm newbie here, so how are You.

I have 3 servers, but only 1 I can access directly from my computer and my network, here is the diagram :

PC SSH Connect (22) -- (3338) 192.168.1.1 --- (22) Serv1 --- (22) Serv2 --- (22) Serv3

The configuration is like that. I can connect directly (SSH or FTP) to server 1 on port 3338.
but if I have to access serv2 or serv3 by ssh it must be through serv1 first.

My question is how to do a ftp tunneling to serv2 and serv3 and thx before for all advise.. cheers