How do you intonate a fixed acoustic bridge? Because I need to do that but I don't know how too. If you need to know anything more about the bridge I can try to help but im not sure.
If it's an acoustic guitar bridge with pins in it, I don't think that you can. You could have the truss rod adjusted, but I don't know if that will solve your problem. You might just need a different gauge of strings.
i dont know much but adjusting theTruss rod wont work...and im pritty sure you cant fix the inoation on an acoustic.
It's not impossible. If the notes are flat on the 12th, raise the action a bit. If they are sharp, lower the action. Intonation on the low frets can be adjusted by raising or lowering the nut. You can also change the strings. Thicker strings go towards sharp when fretted, thinner strings flattens them a bit.
Truss rod adjustments should only be done to set a desired neck curvature, not for dialing in action or intonation. Off course the neck curvature should be right before you try anything else.
Another warning; fiddling with the bridge piece requires some precision. You can easily mess it up. The top nut is a real bastard to get right. You will ruïn it first try even if you are an experienced precision fabricator.
You might just as well consider leaving everything as it is. Most acoustics are a bit off on one or two strings in the high regions. Accept this as a fact of live.
Proper intonation relies upon a myriad of factors, including: a straight fretboard (that hasn't been planed straight during a refret due to bowing that the truss rod cannot correct), proper humidification, proper neck angle and structural stability (a stable top and bridge). You should take it to a repair shop.

Small adjustments in intonation may be made by recontouring the top of the saddle (which will lower the action) or replacing the saddle with one that's been custom intonated.

For more serious offendors:
Once the instrument gets a pass on structural stability, a straight neck and humidification a new bridge can be made with the saddle slot cut in the proper location. Sometimes the original bridge's saddle slot can be plugged and recut in the proper position.

Sometimes on more costly instruments I'll reglue the fretboard (usually closer to the nut) and touch up the top at the soundhole or just plain old replace the fretboard with one of an appropriate scale length to adjust for the dimensional changes that have caused the problem in the first place. This option is expensive and only warranted on valuable vintage instruments (it takes a lot of years for an instrument to dimensionally change from string tension to the point that a neck reset or serious reintonation measures are made neccessary).

I hope this helps.