The weight unit can be changed in MENU > Settings > Units
Click the back arrow in the top left to validate the unit change. The unit change may take a few seconds to be changed on the scale.
*credit to Sylvain of iHealth Labs EU
https://helpcenter.ihealthlabs.eu/hc/en-gb/articles/208054889-iHealth-Core-HS6-How-to-change-weight-unit