The weight unit of measure is changed from the app.
Go to MENU > Settings > Units.
Once the unit of measure has been changed, connect the scale so the change of unit is taken into account. To do this, take a Online measurement.
*credit to Sylvain of iHealth Labs EU
https://helpcenter.ihealthlabs.eu/hc/en-gb/articles/360000007525-iHealth-Lite-HS4S-How-to-change-the-unit-of-measure