When converting a property from personal use back to a rental when it was a rental in the past, you have to adjust the cost basis of the property (structure only) to take into account the depreciation that was taken before.
You reduce the cost basis of the property by the total amount of depreciation taken in the prior years when it was a rental before. Then, depreciation starts over from year 1 for the next 27.5 years using the new, adjusted cost basis.
You will also need to keep a separate record of the prior depreciation taken, as it will come into play in the future when you sell the property.
