Two main factors that affect enzyme activities are temperature and pH value.
Every type of enzymes has their own optimum temperature and pH, where they work the fastest at.
for temperature, if the temperature is too low for the enzyme, they may become inactive, they work slow. Give them their suitable temperature they'll work fast again.
However, if the temperature is too high, the enzyme would be denatured. You cannot use them again.
Denatured enzymes means the enzymes already changes shape of the active site and can no longer bind into substrates and therefore no longer works, no matter if you provide the suitable environment again.
For pH, the concept is same, unless if the pH value is too extreme than the optimum pH, the enzyme will be denatured instead of being inactive.