Convert String value to OffsetDateTime

Question

I have the following code:

   public class Objc{
    
    OffsetDateTime purchaseDate = new OffsetDateTime();
    
    // getter/setter
    }
    ....
    String buyDate = ......;
    
    objc.setPurchaseDate (new OffsetDateTime(buyDate));

How to convert String to OffsetDateTime object properly?