Managed speed is “managed” based on various factors that you enter into the MCDU.
Cost Index (CI) determines if the aircraft prioritises speed to the destination or fuel efficiency. Set this to 0 for fuel efficiency but slower speed, or set this to 100 for the maximum optimal speed but burning more fuel. You can choose any values in between depending on how you want to balance them.
ZFW/ZFWCG determines your aircraft and passengers and cargo weight without the fuel
Block determines your current fuel on board
Flight Level and temperature determines how high you are and what the operating outside temperature would be.
The MCDU calculates the managed speed for all of the phases of the flight based on the inputs above. The managed speed are designed to give you the optimal airspeed based on calculations, if you disagree with it, just use selected mode to any airspeed you want. Otherwise, the managed airspeed is actually the optimal one.
As I mentioned in your other posts, you can’t delete DECEL waypoint because it’s not a waypoint. It’s just a point in the flight plan that tells the aircraft to switch to APPR phase. If it’s not working for you, you can manually activate the APPR phase in the Perf page.
What do you mean by the blue tunnel? Are you talking about the ILS glideslope and localiser? If so, you have to make sure the ILS frequency is entered correctly. Most cases, the sim correctly assigns this frequency from the flight plan. But sometimes on some airports, the frequency entered is wrong.
So when you select a runway in your flight plan’s arrival page, make sure the ILS frequency is also entered in the NAV RAD page. If it is, check your Navigation Display (ND) radar. If the ILS Runway number is correct, that means you’re on the right frequency. Otherwise, if you entered Runway 36 and the frequency, but it’s showing Runway 18 instead. That means you’re on the wrong frequency. At this stage, just google the airport runway ILS frequency and change it in the NAV RAD page. Chances are when you enter the correct frequency the ND will show the correct runway number and you can capture the signal on approach.