Yes, the 2021-2023 SID (35MM) C1 can be converted to Flight Attendant by installing either of the damper upgrade kits listed below.
00.4318.105.000 (Damper Upgrade Kit - Flight Attendant Charger RaceDay2 (Includes complete Damper, Module, Battery, Charger)(necessary power meter/pedal sensor not included) - SID 35 C1-D1+(2021+)
00.4318.115.000 (Damper Upgrade Kit - Flight Attendant USB-C Charger RaceDay2 (Includes Damper, Module, Battery, USB-C Charger)(necessary power meter/pedal sensor not included)-SID35 C1-D1+(2021+)
RockShox service kits and spare parts are best obtained through your local shop or dealer. See our dealer locator, below, to find a dealer near you. If no one is currently listed near you, then please search for local shops via your preferred web browser.
https://www.sram.com/en/dealer-locator
Manuals and additional information about RockShox and SRAM components can be found at our service site, linked below.
https://www.sram.com/en/service
Further questions?
Reach out to Rider Support by Asking A Question at the link below.
https://www.sram.com/en/rockshox/campaigns/rockshox-rider-support