You generally cannot claim Input Tax Credit (ITC) for the financial year 2018-19 as the deadline for claiming it has expired. This applies even after filing your annual return. However, if the self-invoice for RCM (Reverse Charge Mechanism) has only recently been raised, you may still be able to avail the ITC as the time limit for this specific scenario might not have passed.
The ITC on GST paid under RCM now can be availed now as the self invoice would be raised now and the time limit for the same for availing would not be expired.