here you go with the best you can do, that is write a variable in the settings, use a dynamic page and use the command submitOnChange + defaultValue = variable (variable = whatever value you want to enter there, can be another setting like here or an atomicState.value set inside the app (but then don’t forget to make the app run the updated() loop to refresh this default value. Hope this helps.
if(warmerorcooler == "warmer"){
input(name: "AddDegrees", type: "decimal", title: "Add this value to $Thermostat_1 for both cooling and heating settings", required: true, submitOnChange: true)
def set = AddDegrees.toInteger()
input(name: "SubDegrees", type: "decimal", title:"Enter the same value", description: "enter here the same value than above", required: true, defaultValue: set)
if(AddDegrees){
log.info "SubDegrees = $SubDegrees"
}
}