Himself asked, himself and the answer found )
/wp-content/plugins/woo-wallet/templates/wc-endpoint-wallet.php
<input type="number" step="10" min="<?php echo $min_amount; ?>" max="<?php echo $max_amount; ?>" name="woo_wallet_balance_to_add" id="woo_wallet_balance_to_add" class="woo-wallet-balance-to-add" required="" />
change: step=”10″