I want to use the heating tape (constant wattage) and I was told that I should use RCD for the safety. I am new to RCD so I wanted to double-check if this is a correct way to wire the RCD with the power supply and the heating cable. Your help will be greatly appreciated. Thank you.
No no no, you can't directly feed a branch circuit load off the pictured 63A breaker!
A breaker that size would be appropriate to feed a subpanel (e.g small secondary consumer unit), and inside that, you could have regular breakers of appropriate size (13A or 16A) to feed to the heating tape. Every circuit thus fed would inherit the RCD protection from the pictured breaker.
It is normal in Europe to put the RCD on "the whole house" or a significant fraction of it. So 63A is a perfectly normal size for a 30ma rated RCD. The purpose of the RCD is reduce house fires by catching partial-short ground faults, and also providing limited protection to humans against severe shocks. This contrasts with American practice to put one 15-20A RCD (GFCI) per branch circuit, and the RCD is much more sensitive at 5 to 8 milliamps. The primary purpose of that RCD is to protect humans from shocks of modest severity. (A shock that stuns, also kills if it has knock-on effects of falling, drowning etc.)
So if you are powering a modest amount of heat tape (<2500 watts) and your primary purpose in RCD is due to an elevated risk of electrical shock, you may want to opt for a branch-circuit-sized 6ma RCD.