While purchasing the first ticket, you can mark the Return button, or after purchasing one-way, you can re-enter the system and purchase the return tickets by examining the reverse route sign with the reverse route sign.
When you search for flights between Bangkok and Hong Kong, all active companies and flight times on the date you entered are listed. You can find the cheapest flight tickets by sorting this list by price.
The most frequently used airline companies from Bangkok to Hong Kong are generally
TAP Portugal,
American Airlines,
Hong Kong Express Airways,
Thai Airasia,
Air New Zealand,
Thai Airways Intl,
Singapore Airlines,
Emirates,
KLM,
Qatar Airways,
Rheintalflug,
Cathay Pacific,
Vietjet Aviation,
Hong Kong Airlines,
Bangkok Airways
are companies.