There are a number of very good Novenas available online. I have chosen three, each with a slightly different emphasis.
If you want to finish the Novena on the eve of Pentecost, you would begin on Friday 14th May. If you want to finish it on Pentecost Sunday itself, you would begin on Saturday 15th May.
- Ecumenical Novena to the Holy Spirit: https://cmax.tv/pentecost
- A Psalm-based Novena: https://www.thykingdomcome.global/sites/default/files/2021-03/RC1053_TKC_Novena2021_V5-WEB.pdf
- Walsingham Holy Spirit Novena: https://www.walsingham.org.uk/wp-content/uploads/2020/05/holy-spirit-novena.pdf