There's no way to request a manual increase, but there are two paths to a higher amount:
Path 1: Wait for the automatic 5% growth (most reliable)
Every month you pay your second Split Pay payment on time, Split Pay's share of your bill grows by 5% the next month — up to a 50/50 split. This happens without any action on your part.
Path 2: Reapply (a fresh application for the amount you need)
This is a fresh evaluation of your full financial profile. If you reapply within 30 days of your last decision, the review uses the same financial snapshot, so the result is usually the same. Your approval could go up, stay the same, or go down — see the FAQ on Will I get the same approval amount if I reapply?.
Worth knowing: if your bill amount increases but stays under your current approval, you don't need to do anything — Split Pay automatically adjusts within your existing limits. Reapplying is only necessary if your bill exceeds what you're currently approved for.