You can buy an AXS power meter from any SRAM authorized dealer. Or, you can place your order directly from SRAM.com and the power meter will be delivered straight to your door.
HOW TO INSTALL A SRAM AXS POWER METER
The spider-based power meters on RED and Force attach to AXS cranksets using a simple 8-bolt interface. To install one, remove your driveside crank arm using a hex wrench long enough to apply the 60 Nm of force required to back out the fixing bolt.
Then remove the eight Torx T20 bolts that attach the Force crank spider or RED chainring assembly to the crank. If you are upgrading a Force crankset, we recommend removing the chainrings using a Torx T30 wrench before removing the eight spider fixing bolts.
Lift the non-power spider or chainring assembly off the crank and replace it with the power meter version. Install the eight new Torq T20 bolts supplied with the power meter and torque them to 4 Nm. If you have a Force AXS or a RED 1x crankset, now install the chainrings and torque the four Torx T30 fixing bolts to 12 Nm.
Reinstall your crankset and torque the 8mm hex fixing bolt to 54 Nm. Just be sure to place the chain on the small chainring before doing this.