Arri Alexa

Use this AlexaV3_K1S1_LogC2video_Rec709_EE_Luther3d.Preset generated using Arri LUT Generator. This DS Preset (LUTs Effect) converts Alexa Log C to ITU709 color space.

Steps in 4:2:2, not tested, but it should work

1. Link Alexa Log C material as "ITU 601/709" in the capture settings.
2. Apply LUT as clip effect to individual clips or as source side effect to Alexa Log C footage.
3. Color correct as usual.

Steps in 4:4:4

1. Link Alexa Log C material as "linear" in the capture settings.
2. Apply LUT as clip effect to individual clips or as source side effect to Alexa Log C footage.
3. Apply LUTs Effect ITU709 Log to Lin preset as track effect. Make sure no other footage than Alexa is on the track.
4. Color correct as usual, between two LUTs.

Advanced Discussion

Why not create a Log C to Lin LUT for use in 4:4:4? That would get rid of the Log to Lin track effect. Because DS color corrector as of version 10.5 is calibrated to work with gamma corrected video.