The truth is that you didn't.

You tune all the instruments to match each other before the performance and just go with it. Pick the hardest instrument to tune (piano, organ, or oboe) and tune to that.

Older pipe organs from the 1600s have been found to have an A that ranges from 380Hz on one organ to 530Hz on another. Since they were never played in the same place, it didn't matter except when you are trying to sing and it's near the edge of your range.

Over time as instrument manufacture began to be more standardized and a musician might perform with different groups, it started to matter more, but there were still regional variations. So long as the players tuned their instruments to match each other before the performance it worked OK.

The tuning fork was invented in 1711 which gave much more stability to frequency comparisons. Unlike violin strings which change pitch with humidity, and winds that change frequency with the temperature, a tuning fork is almost constant. Prior to electronics, that's what piano tuners carried with them. (When I bought a guitar in 1986 it came with a tuning fork.)

In Mozart and Handel's time musicians settled on an A that we've later measured to be about 422Hz. There are some modern performers who retune their instruments to match the old frequencies when performing old music.

Over time this began to creep up in a sort of "tuning arms race" through the 19th century as each orchestra tried to get a more brilliant sound. At one point it had creeped up to A=450Hz in some places, but it eventually is settled back to A=440Hz.

If you get a really old piano, they were not designed to handle modern tuning and can collapse if you tune them up to modern levels.

Source A.H. Benade: Fundamentals of Musical Acoustics.