Finding an excellent piano tuner can be a challenge. Look for someone who has good contemporary references that you can check. The track record is crucial.
Step1
Hire a professional to do the job.
Step2
Finding a good one is often a difficult task.
Step3
Get a recommended tuner from the music dept. of a nearby college or university.
Step4
Realize that "Ear Training" development, understanding "Harmonics" and how the "Overtone Series" function in the tuning process are major skills to possess.
Step5
Mastery of specialized tools are required in this trade.
Tips & Warnings
The advanced musician is trained to 'hear' the "Overtone Series".
The piano tuner uses this skill to tune and match the sounds of each one of the 88 strings. Much time is needed to learn and refine this skill.
A "piano-tuning" school will include this within its curriculum.
Highly refined ear training develops over a lifetime. A properly trained young person can possess or be taught this.
Be prepared to service, replace or repair worn and broken portions of the piano when it has been opened for examination.
Consider budget limitations depending on the age and value of this particular instrument.