When using FIR Designer M for multi-way, how you use the “Find peak” depends on how you took the measurements.
If your measurement system delay was locked when taking measurements across all the drivers, the relative delay between drivers is in the measurements, and using “Find peak” on each measurement will loose the relative delay. In this situation, you could complete your design, put all the processing into your DSP then re-measure and tune the channel delays. Alternatively, use “Find peak” on one of the drivers – say the HF – and manually apply the same delay (on the “Import tab”) to the other drivers. In this way the relative delay between drivers (in the measurements) is not lost. You can complete your design and you won’t need to re-measure and tune delays.
If your measurement system delay was not locked when taking the measurements across all the drivers, then it doesn’t matter if you use “Find Peak” or not. You will still have to re-measure and tune the relative driver delays anyway.
“Find peak” it’s useful for taking out any high phase slope, which is the consequence of delay in the measurement, before working on designing the processing.
I’d also suggest looking at the “FIR DESIGNER M (Multi-way) | Overview” video on https://eclipseaudio.com/fir-filter-design-tutorial/