First of all you need to make and install OpenSSL 1.0.2r from source.

sudo apt install build-essential checkinstall zlib1g-dev -y

cd /usr/src

wget https://www.openssl.org/source/openssl-1.0.2r.tar.gz

tar -xvzf openssl-1.0.2r.tar.gz

cd openssl-1.0.2r

./config -d --prefix=/usr/local/ssl --openssldir=/usr/local/ssl shared zlib

make
make test

make install

nano /etc/ld.so.conf.d/openssl-1.0.2r.conf

Add this line and save:

/usr/local/ssl/lib

sudo ldconfig -v

mv /usr/bin/c_rehash /usr/bin/c_rehash.BEKUP
mv /usr/bin/openssl /usr/bin/openssl.BEKUP

export PATH=$PATH:/usr/local/ssl/bin

Link binaries to path:

sudo ln -s /usr/local/ssl/bin/c_rehash /usr/bin/c_rehash
sudo ln -s /usr/local/ssl/bin/openssl /usr/bin/openssl

Restart.

sudo shutdown -r now

Check OpenSSL path, should return '/usr/bin/openssl'.

which openssl

Check OpenSSL version, should return 'OpenSSL 1.0.2r 26 Feb 2019'.

openssl version

Modify '/usr/src/kamailio/src/modules/tls/makefile'.

Change this:

ifneq ($(SSL_BUILDER),)
	DEFS += $(shell $(SSL_BUILDER) --cflags)
	LIBS += $(shell $(SSL_BUILDER) --libs)
else
	DEFS += -I$(LOCALBASE)/ssl/include
	LIBS += -L$(LOCALBASE)/lib -L$(LOCALBASE)/ssl/lib \
			-L$(LOCALBASE)/lib64 -L$(LOCALBASE)/ssl/lib64 \
			-lssl -lcrypto
	# NOTE: depending on the way in which libssl was compiled you might
	#       have to add -lz -lkrb5   (zlib and kerberos5).
	#       E.g.: make TLS_HOOKS=1 TLS_EXTRA_LIBS="-lz -lkrb5"
endif

To this:

DEFS+=	-I/usr/local/ssl/include
LIBS+=	-L/usr/local/ssl/lib \
		-lssl -lcrypto

Make clean, make and make install:

cd /usr/src/kamailio/src/modules/tls
make clean
make
make install