Reactivating a dormant account isn't a one-size-fits-all process.
Steps
Start by contacting your bank and asking about the account's specific status: is it inactive or dormant, and what's required to reactivate it?
The bank will likely need to update your information and verify your identity, and may require you to visit a branch or complete a specific procedure depending on the length of time it's been inactive and the account type.
Don't transfer funds to the account until you're sure it's ready for receiving and normal operation, and inquire about any existing fees or restrictions before reactivating it.
The figures, fees and limits in this answer vary by bank and change over time — confirm them with your bank or the official source before acting.