To replenish BTC you must go to the correct menu:
https://kuna.io/funds#/deposits/btc
During registration for each account, the exchange will generate a unique wallet number.
For deposits, you can simply copy your wallets number and make a transaction like a transfer of BTC.
Features of BTC deposits:
1) There are no restrictions on the type of BTC wallets.
2) Funds appear on the account after three confirmations on the bitcoin network.
Tracking is possible in any blockchain browser, for example, https://blockchain.com
3) There is no commission on deposits.
4) The minimum deposit amount is 0.001 BTC