how to lower ph soil temporarily/short term?

i’m growing ixora(santan) which apparently needs slightly acidic soil (5.5-6.5 ph). i already repotted it but the soil is neutral.

I bought elemental sulfur and ammonium sulfate already, and will work on a separate soil once I get them delivered. I know it takes months before it actually acidifies the soil, so what do i do for the mean time so my ixora is getting the right conditions?