The same way as the previous one. Once you have obtained your approval letter (POE), you will need to exit and re-enter Canada in order to activate the new work permit. You can do this by flying out and back to Canada again, or flag-poling.
Flag-poling is essentially the act of leaving Canada via a border crossing, only to immediately return. It is a common strategy used by non-residents in Canada to activate their visas. This essentially entails crossing a border (generally to the US), which is sufficient to activate your IEC work permit. Alternatively, if you’re up for a little bit of travel and adventure, you could use it as an opportunity for a weekend away!