Trim the worst of the damage off, rich enough products, careful choice of ingredients, way more leave in conditioner than you think you need, regular deep treatments, a little patience!! Good ingredients for damaged or porous hair include coconut oil, hydrolysed protein, ceramides and panthenol.

Be careful with up dos, they can also be damaging especially to hair that is already weakened. If you use them be sure they are loose not tight, use super gentle tools and ties like satin, don't wear the same style regularly.

Do be aware that hair is dead so you cannot repair it or make it healthy again .All you can do is reduce the porosity, patch repair the surface (temporary) and protect from further damage.
2a-2c, medium texture, porous/ colour treated. Three years CG. Past bra strap length heading for waist.

CO-wash: Inecto coconut/ Elvive Volume Collagen
Treatments: Komaza Care Matani, coconut/ sweet almond/ fractionated coconut oils, Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss Ultimate Volume, various Elvive
Styler: Umberto Giannini jelly, Au Naturale styling gelee
Flour sack towel, pixie diffuse or air dry.
Experimenting with: benign neglect