At first level, you can't yet do it
As a third level spell is involved, it requires a cleric of not less than 5th level of experience to manage to create such fluid. (DMG, p. 114)
If you can get a higher level cleric to help you ...
From the DMG you will find the following requirements:
- A holy water font is required (details in the DMG at pages 114/115).
What your acolyte must do is find a temple/shrine/church/holy ground
that includes a holy water font.
Then ally with or convince (or
pay) an NPC cleric that can cast the 2nd and 3rd level Chant and
Prayer to perform the ceremony. Your first level cleric could
assist. Your acolyte can, however, bring various
receptacles/containers/vials, as noted below.
Spells that must be cast over the font:
- create water
- purify food & drink (the water) or its reverse
- bless or its reverse
- chant ( 1 full turn)
Once created, the holy/unholy water cannot leave the font far more
than a turn without losing its efficacy unless it is placed within
specially blessed/cursed vials of crystal - either rock or special
leaded glass. Each empty vial is worth 2-5 gold pieces. (DMG p. 115)
As there are a lot of details involved in this process, you'll want to work with the DM on all of the details so that preparation, preparing the containers to fill with holy water, interaction with the NPC, and the ceremony itself all come together.