Please see link above to video for IBC' guidance on how to complete your PV ballot.
More details here-
If you will be going away before or very close to the date of delivery and will still be away on election day then you may want to consider a proxy vote or depending on timings your postal vote may be able to be sent to another address. If you will be back by election day then it is still possible for you to complete your postal vote and hand it in to your usual polling station or Grafton House up to 10pm on the day of the elections. Postal votes received after this time will not be able to be counted.