I have a toshiba estudio 2500c. I have error code C3B0. How do I fix it without calling a service person?

That depends on the printers model
One could be;
Check to see if the waste bottle is overfull.
If yes, the waste toner will be backed up into the waste tubes, first affecting the primary transfer cleaner unit, then the black drum cleaning unit, then the color drum cleaning units.
Or;
Developer unit • Check if the developer unit is installed properly. • Check that the developer unit and coupling on the equipment side are properly engaged. • Check that the mixer of the developer unit is rotated. • Check if the developer material is too dark visually. • Check if the amount of the developer material is too large or too small. • Remove any toner or dust on the ATC sensor connector and the drawer connector of the process cover. • Remove any toner or dust on the EPU sensor connector and the drawer connector on the equipment side.
Or;
Auto toner sensor Harness LGC board • Check the connectors and harnesses between the auto toner sensor and LGC board (CN364). • Check if there is any foreign matter such as toner in the connector of the auto toner sensor. Remove if there is and reconnect it.

https://printcopy.info/?mod=erc&brand=Toshiba&model=e-Studio+3005AC&code=C3B0

https://www.google.com/search?q=toshiba+error+code+c3b0&client=firefox-b-d&ei=ML2oYMHaMZCXsAenyKZY&oq=toshiba+error+code+c3b0&gs_lcp=Cgdnd3Mtd2l6EAMyBAgAEBM6BwgAEEcQsAM6BggAEAcQHjoICAAQBxAeEBNQ6bQEWMXBBGC52gRoAXACeACAAbMBiAG9BpIBAzUuMpgBAKABAaoBB2d3cy13aXrIAQLAAQE&sclient=gws-wiz&ved=0ahUKEwjBssiG7NzwAhWQC-wKHSekCQsQ4dUDCA0&uact=5

Check home position sensor connector, replace home position sensor, replace SLG board

Here is the verbage for the error code at this link
http://printcopy.info/?l=en&mod=erc&brand=Toshiba&model=e-Studio%202006&code=C413

In the interim you may try the following one time to see if it is a false error... Hold "0" and "8" while turning on machine.....continue holding until machine enters service mode. Enter "400" press enter. Enter "0" press enter. Power off / on. If code returns, machine needs parts replaced. Contact your Toshiba technician (there should be an 800 number label on the unit for service. Do Not keep resetting, may cause damage to Fuser Unit.

Toshiba eStudio 355/455 Full Service Manual - Tradebit.com

https://www.tradebit.com/.../155135538-toshiba-estudio-355-455-full-se...
Download Toshiba eStudio 355/455 Full Service Manual ... Configuring DepartmentCodes Configuring ... TSB-1013: C440 Error - Countermeasure .... DIG-ACC-145: MJ-1025 Bracket Change to Enable Installation on e-STUDIO205L/255/305

Normally the error code is display on the panel...

It will depend on which error code displayed?

08 on 400 strart 5 or 9 next '0' enter

Only a technician can decipher the Call for Service error.

This is a pretty complicated issue/problem. there are 5 pages devoted to this issue in the service manual. This issue would be best handled by a technician. but you could try the following....
[CA00] Color registration abnormality
<Color toner low density>
Turn on the copier holding down 0 and 8 and wait till it boots up into its service mode..then enter code 2692 “Prevention of color toner low density / change the zero to 1.
Then change code 2693 “Prevention of color toner low density / Judged number of sheets setting” value to 40 (default 20).
Make sure you have cleaned the main charge units by fully extending the rods with the green handles for each color.(open the front door) and use the plastic wand attached to the front door to clean the laser glass for each color..there is a small **** under each color unit to slid the wand into..felt side down on the wand.

Like I said there are several other complicated ways of fixing this.