Back in the day it was common practice for a baby suffering reflux to have their cot elevated at the head end. As the advice is now to have baby lay flat how can we address the issue of reflux?

Red Nose has comprehensive information about Gastro-oesophageal reflux (GOR) & Gastro-oesophageal disease (GORD)
This includes the following information.
Gastro-Oesphageal Reflux Disease (GORD) occurs when the reflux of gastric (stomach) contents causes troublesome signs and/or complications, that is, when GOR has an adverse effect on the well being of the baby, for example, when the GOR causes poor weight gain or complications such as oesophagitis or respiratory signs. This requires medical assessment before a diagnosis of GORD is made
Regurgitation in children is defined as the passage of refluxed contents into the throat, mouth or from the mouth. Other terms include “spitting up”, “possiting” or “spilling’. It is a characteristic sign of reflux in infants but is not diagnostic of GORD

Babies with GOR should be placed to sleep on their back from birth on a firm, flat mattress that is not elevated.
Elevating the sleeping surface for back sleeping babies does not reduce GOR and is not recommended.
If a baby is in a tilted cot, further hazards may be introduced into the sleeping environment. When tilted, babies are more likely to slip down the cot and become completely covered by bedding, or if a pillow is used to elevate the baby, pillows become a suffocation hazard.
In babies with GOR, the risk of sudden death when baby is in the tummy or side sleeping positions outweighs any benefits of tummy or left side positioning of babies.
If, for a rare medical reason a baby must be slept in a position other than the back position, medical staff should advise the parents in writing and provide information about the other ways parents can use to reduce the risk of SUDI.
https://rednose.org.au/article/my-baby-has-reflux
The following has been suggested by Red Nose as some ways of managing reflux in babies, but definitive management for reflux & GORD would need to be determined by doctor.

Breast feeding. Babies who are breastfed have less GOR
Eliminate smoking. Eliminating environmental tobacco smoke (ETS) is important for many baby health outcomes. In adults, cigarette smoking is a common cause of gastro-oesophageal reflux, and ETS from parental smoking may also be a cause of GOR in babies.
Thickened feeds. Two critical systematic reviews of the literature suggest that thickening of feeds is helpful in reducing the signs of GORD. Results show that frequency of regurgitation and vomiting is reduced and increasing weight gain can be achieved by thickening feeds.
Pacifiers (dummies) used for non-nutritive sucking have no effect on acid and non-acid GOR and thus can be used in preterm infants with GOR.
https://rednose.org.au/article/sleeping-position-for-babies-with-gastro-oesophageal-reflux-gor

https://rednose.org.au/article/why-back-to-sleep-is-the-safest-position-for-your-baby