Return to player (otherwise known as ‘RTP’) is a term used by casinos and online betting platforms to describe the percentage of any wagered money that will be paid back to players over time from slot machine games. Calculated as an average based on at least 1,000 plays, it’s an indicator of the long term performance a player could expect to see from playing that particular game – but of course this doesn’t account for what could happen in the short term.
With Bustabit having a 1% house edge the RTP is 99% for every 1 BTC wagered the expected amount that you'll get back is 0.99 BTC but that is not always the case because there can be times where you'll win earlier than expected. You have the choice to stop while you're ahead to avoid those losses from occurring.
To answer OP's question there's no way to increase the RTP on Bustabit. They had a bonus on the older version but it looks like it's removed on v2 .