I need to know the concentration of descaling tablets to water to descale my cva 610 coffee maker. The instruction manuel says to fill the water container HALF WAY with correct solution of descaling agent and water. How many tablets to how much water? Thank you

Try a manual reset.

https://www.google.com/search?q=Miele+610+reset

Also, I just found the technical manual for the 610

https://cagrimmett.com/justanswer/CVA610.pdf

..

It needs the brew unit cleaned - descaling is mainly for the heaters. The Brew unit tablet (the one the size of a sweetart) is used to clean just the brew unit. In the maintance menu your will find clean brew unit - follow the bouncing ball

1. If you can get steam/water from your steam spout.
   

2. Fill your tank and add descale solution.
   

3. Descale according to the instruction for the unit.
   

4. After descale and rise are complete refill your water tank.
   

5. Your system should now work as normal.
   

Note: If you do not have a descale solution, run the above with just water. Remember to descale when you obtain a descale solution.

Have you Cleaned the Brew unit? The descale Tablets are to clean and descale the internal plumbing - the cleaning tablets are to remove the oils from the brew unit. If clogged the water will not flow through , instead it will dump into the drip tray.

Fill with water again , use vinegar or lemon juice , Use distiled water always for brewing and descaling .

THIS INSTRUCTIONS ARE FOR THE MIELE CVA 615,

The coffee system must be descaled regularly. The time period depends on
the water hardness set. The appliance will display a reminder message and
will eventually lock if not descaled. The message window will first display:
"DESCALE AFTER COFFEES: 100".
This message will appear until the appliance is descaled or locks. When
the count is down to zero, the appliance will lock and the message
window displays: The appliance can only be used again
once descaling has been performed. Let the machine cool before
descaling. Remove the sleeve of the steam nozzle to avoid damage from
the descaling agent. Only use the enclosed descaling tablets for descaling.
The descaling tablets are specially designed for descaling this coffee
system. Other agents may damage the machine and affect the taste of
the coffee and hot water. The descaling tablets can be purchased
from Miele.
To prevent damage to the exterior of the machine wipe up any descaling
solution spills immediately! Add 2 liters of water to the water tank. Dissolve two of the enclosed
descaling tablets in the water.
^ Close the water tank and insert into position.
^ Close the door. The descaling will take place in the
automatic descaling program.
Automatic descaling
^ Turn the program selector
counterclockwise to the "Program
mode" position.Press e, to select "Descaling" with the asterisk. Press ENTER.

Purchase some citric acid based descaling tablets,
Fill the water tank to the very top and add the tablet to the water
Insert the cleaning disc
Press and hold the button to start the descaling program
Continue to refil the watertank as necessary until the descaling light goes off (This can take over an hour on a Bosch machine - or about 20-40 mins on a Bruan).

You have to buy descaling tablets from miele.  You turn the knob to program mode and keep pushing the enter button until you get to descaling.  You put two descaling tablets into your water reservoir and replace into unit.  Put containers under the steam valve and the hot water wand. Press enter.  Turn steam valve al the way on.  Keep an eye on the containers.  The process takes about 30 to 40 minutes.  The message will appear 'Descaling finished." Turn steam selector to O and press enter.  Display will read "rinse machine, fill watertank.  Fill tank and return to machine.  Place empty containers beneath hot water dispenser and steam nozzle again and turn steam selector fully on. Allow water to run through system completely.  When process is finished, display will read "Rinsing Finished."  Turn steam selector to O and press enter  Program selector is on Program Mode and display will read Descaling, Timrt, unit is no descaled and ready to use.  Turn program selector to on.

You need to descale the machine with descaling solution.
look at following link for instructions

DELONGHI