Even if they're clean, tissues are not recyclable. This is because they are made from paper with very short fibres – and in order to be useful for recycling into something new, the fibres would need to be longer. Paper can only be recycled a certain number of times because the fibres get shorter each time. Please put tissues in the general waste.
If you suspect or know that you might have COVID-19, there are specific guidelines to follow for disposal of 'personal' waste like used tissues. Take a look on COVID-19 Personal Waste (opens in a new window).