In documentation’s FAQ item no 3 explains how can you accomplish behaviour where bid increment is going up in steps different than $1 – https://wpinstitut.com/auctions-for-woocommerce-documentation/
Basically you need to copy bid.php template to your child theme\woocommerce\single-product\bid.php and make following change
step="<?php echo ($product->get_auction_bid_increment()) ? $product->get_auction_bid_increment() : '1' ?>"
This will make steps to increment by value set in min bid increment in auction details in wp-admin for example if you set min bid increment to $10 bids will be $10, $20, $30, … If template folder does not exist in your child theme you need to create it manually (via FTP or some kind of File Manager).