There are many avenues for inmates to file suit. One are the resources available in the jail another are organizations which help I mates with legal council
Contact local consel
Here is a link to the prison litigation reform act.
Must comply with this before any suit can be filed. Have him file grievances right away.
In addition to what my distinguished colleagues have said, kindly note that inmates file pro se civil suits all the time. There are numerous inmate colleagues as well as the prison library volunteers available to assist pro se inmate litigants. All the best.