In this paper, a design and simulation of a reconfigurable Intelligent Reflecting Surface (IRS) based Frequency Selective Surface (FSS) working at 3.5 GHz is introduced for 5G communication below 6 GHz. In the introduced design, a compact and interconnected H slot unit cell is adopted in which FR4 substrate is used as a substrate material and copper as the conducting material. For designing the reconfigurable IRS, two and four diodes are incorporated in the structure of the FSS. The IRS approach has been introduced to help achieve dynamic manipulation of the reflected electromagnetic waves by diode switching. The simulation has proved that there is a phase shifting amounting to about 13° using the four-diode IRS while there is a phase shifting amounting to only 6° using the two-diode IRS. Thus, the proposed structure is considered to be cost-effective, easy to operate, and very efficient in controlling adaptive electromagnetic waves in 5G wireless communications and IRS-based communication systems.