Water is constantly running into the toilet bowl and I am having difficulty to remove the lid to have a look inside the cistern. How do you get the lid to determine the problem it why the toilet continues leaking water? We have tried to unscrew the seal around flushing press components without success.

The only place I can think of is the steel bolts in the bottom that hold the cistern to the toilet bowl. The fix, you could empty the cistern tank, remove the bolts and replace them. Or you could drain and dry the tank inside and cover the bolts with clear silicone. EXCEPT, it appears to be a macerator toilet. The inside is supposed to be ceramic. You would have to fully strip it and check.

How does Tecma toilet work?
The water inlet device delivers clean water to the inside of the toilet bowl. The macerator pump, integrated in the ceramic toilet, grinds the waste and then moves it to the black water holding tank. The flush cycle is activated by pressing the control panel buttons.

TECMA TECHNICAL HANDBOOK a reference guide for designers ...

https://www.google.com/search?q=%22tecma%22+toilets+rust+in+water

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You have to check inside the cistern. Various valves may be contributing to leaking and constant running.

See this article:
https://www.familyhandyman.com/plumbing/toilet-repair/parts-of-a-toilet/view-all/

With lid removed, look down into it and remove and replace the black rubber thing in the center. This is the flush valve and is worn to the point where is no longer provides a tight seal allowing water to pass and run into bowl. Also, could be something underneath it not allowing it to seat properly.

toilet will need syphon replacing. the lid should lift of the cistern, some have the push buttons screwed down to the syphon and to remove them just turn the ring around them anti-clockwise.

It is likely that the leakage is being caused by a worn-out flapper or seal (the part the flapper seats on). You can buy after-market kits that have replacement parts. What is the make and model of your toilet?

IT SEEMS TO ME THAT THE BALL-**** (FLOAT SWITCH) IN THE CISTERN IS SET TOO HIGH UP. THERE ARE MANY DIFFERENT MODELS BUT ALL SHOULD BE EASILY ADJUSTED. HAVE A LOOK INSIDE THE CISTERN AND ADJUST THE FLOAT SO THAT THE WATER STOPS AT A LOWER LEVEL. IF THE WATER IS CONTINUOSLY FLOWING INTO THE CISTERN WHEN FULL YOU MIGHT NEED A NEW INLET WASHER

check the type of fill valve that you have in the tank and check with a plumbing shop or better yet check your local lumber company as
they usually carry toilet replacement parts and you can read the instructions on how to adjust the one you have

If water is constantly running into the cistern you will need to change the rubber washer in the shut-off valve. Washer kits are available from most DIY stores. Turn the water off at the isolating stop-****. Unscrew the end of the inlet valve (watch out that any springs etc. don't ping out) change teh washer and reassemble in reverse order.

replace the flapper