These low-cost LoRa boards often have poor frequency accuracy, which can make acquiring a weak signal difficult - although once acquired, the AFC will automatically track it.
However there is a facility within the Gateway.txt config file to compensate for an offset in the frequency reference:
PPM_<n>=<Parts per million offset of LoRa module.
To set mine, I set up a second LoRa module as a dummy HAB transmitter and measured its average frequency with a frequency-counter. Then I adjusted the PPM_0 parameter so that my receiver agreed with the counter (I think I ended up with PPM_0=-12 or something similar)
However, if you don't have a convenient local test-source, you could study the Receiver-reported frequencies on the Grafana chart for a flight you're following and see how your frequency compares. For example, looking at "ZURG" from last week:
Here you can see that G8HIK-L (in dark red) is showing a few kilohertz lower than the others - that's because his TTGO receiver doesn't have a PPM adjustment facility (as far as I know). But knowing, this, he can manually set his frequency a few kHz higher than expected (although it's still reported to the Sondehub as his set frequency).